Attention has been focused on a technique for forming a transistor (a thin film transistor (TFT) or a field-effect transistor (FET)) using a semiconductor thin film formed over a substrate. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image device (display device). As semiconductor thin films applicable to the transistors, silicon-based semiconductor materials have been widely used, but oxide semiconductors have been attracting attention as alternative materials.
For example, a technique in which a transistor is fabricated using an In—Ga—Zn-based oxide semiconductor is disclosed (see Patent Document 1).